1. Field of the Invention
The present invention relates to an X-ray examination device, including an X-ray source and an X-ray detector, for forming an X-ray image of an object to be examined by exposure of said object to X-rays, an X-ray filter, which is arranged between the X-ray source and the X-ray detector for filtering the X-rays passing through said object, and adjusting means, which are connected to the X-ray filter for adjusting the X-ray filter, which adjusting means comprise a graphics device, cursor control means for defining a region of interest in an image of said object, displayed on said graphics device, and processing means, which are connected to the X-ray filter, for calculating the region of interest and adjusting the filter accordingly, the X-ray filter including a plurality of filter elements having an X-ray absorptivity which can be adjusted by controlling a quantity of X-ray absorbing liquid within the individual filter elements.
2. Description of the Prior Art
Such an X-ray examination device is known from the international patent application WO 98/27867.
The known X-ray examination device uses, among other alternatives, transparent passages as filter elements, which are aligned at right angles to the direction of the X-rays. Each passage is filled alternately by means of pumps with a substance, which is either transparent to X-rays or non-transparent thereto. Thus a contour can be formed in accordance with a region of interest defined by an operator.
The known X-ray examination device has several disadvantages. One of them is that the passages only allow for a rough control of the filter, since the accuracy with which the region of interest can be reproduced by the filter elements is not only limited by the size and form of the passages, but also by the separation line between the transparent and non-transparent substances. Furthermore a large amount of pumps are necessary to fill all individual passages, which raises the complexity and costs of the device. On top of this filling, the passages alternately with the transparent or the non-transparent substance requires several fillings per passage, which is time consuming and makes the control difficult, thereby further raising the overall complexity and accompanying costs.
The invention aims at providing an X-ray examination device of the type described above, which does not have these drawbacks.
The X-ray examination device according to the invention is characterized in that the filter elements are capillary tubes, and means for applying electric voltages to the individual capillary tubes are provided for controlling the quantity of X-ray absorbing liquid therein.
The small size of the capillary tubes makes it possible to define a region of interest in many different shapes thus allowing for fine-tuning the filter elements. The control is performed by applying electrical voltages, making the use of large mechanical elements, such as pumps, redundant.
It must be noted that an X-ray examination device, including an X-ray source and an X-ray detector, for forming an X-ray image of an object to be examined by exposure of said object to X-rays, an X-ray filter, which is arranged between the X-ray source and the X-ray detector for filtering the X-rays passing through said object, and adjusting means, which are connected to the X-ray filter for adjusting the X-ray filter, the X-ray filter including a plurality of filter elements having an X-ray absorptivity which can be adjusted by controlling a quantity of X-ray absorbing liquid within the individual filter elements, wherein the filter elements are capillary tubes, and means for applying electric voltages to the individual capillary tubes are provided for controlling the quantity of X-ray absorbing liquid therein, is in itself known from U.S. Pat. No. 5,625,665 from the same applicant. The known device lacks the adjusting and processing means of the device according to the invention. In the known device the filter elements are adjusted automatically on the basis of brightness values of the X-ray images and/or on the basis of the settings of the X-ray source.
Contrary to this according to the invention adjustment of the filter elements can also be performed directly by the operator. By means of a graphics device and cursor control means he or she can define the desired region of interest in an image of the object which must be subjected to the X-rays, or, alternatively, should be screened therefrom. Thus the X-ray examination device according to the invention allows for fine tuning the filter in a variety of ways.
According to a first preferred embodiment of the X-ray examination device according to the invention the capillary tubes are aligned essentially parallel to the X-rays emanating from the X-ray source. According to a second preferred embodiment of the X-ray examination device according to the invention the capillary tubes are aligned essentially parallel to one another. In both embodiments the region of interest is build up in the filter by means of xe2x80x98X-ray absorbing dotsxe2x80x99 formed essentially by the cross section of the capillary tubes. This cross section being very small the fine tuning possibilities are further enhanced.
In a further preferred embodiment the capillary tubes are filled with one liquid. According to the X-ray examination device of the invention only one liquid suffices to create the desired filter. This greatly simplifies the control and enhances the speed of adjustment. According to an elegant embodiment of the X-ray examination device according to the invention means are provided to control the height of the liquid in the capillary tubes based on the degree of overlapping portions in the region of interest defined on the graphics device.
According to an alternative embodiment means are provided to control the height of the liquid in the capillary tubes based on the pressure exerted on the graphics device during definition of the region of interest on the graphics device. Both embodiments allow for a quick and user-friendly way to influence the degree of absorptivity over de region of interest. Preferably the adjusting means comprise a touch screen, which incorporates both the graphics device and the cursor control means and allows for easy and comfortable navigation by the operator. Most preferably the touch screen is pressure sensitive thereby facilitating local adjustment of the X-ray absorptivity of the filter by locally exerting varying amounts of pressure while drawing the region of interest on the touch screen.
According to a still further preferred embodiment the processing means are arranged to calculate a region of interest based on an open contour by calculating the missing part and closing the contour, the closed contour defining the region of interest. Alternatively the processing means are arranged to calculate a region of interest based on a line and a certain area surrounding the line. In practice these will be useful options to quickly and easily define a region of interest.